Neuroblastoma is the third most common cancer of childhood, with over 500 new cases diagnosed in the US each year. Prognosis for children with advanced disease reamins dismal despite the use of increasingly aggressive chemotherapeutic regimens. The random occurrence of most cases of neuroblastoma and the lack of associated chromosomal abnormalities has hindered the identification of so-called "neuroblastoma genes". Thus, our recent experience which suggests that girls with Turner's Syndrome (TS) are predisposed to develop neuroblastoma and related tumors may be of interest. We hypothesize that a tumor suppressor gene is present on the X chromosome and that loss of an X may be a first step in neural tumor development. We propose to screen a cohort of girls with TS for neuroblastoma using well validated urine assays in order to strengthen this association. Additionally we will compare karyotypes of neuroblastoma in TS patients, both with their constitutional cytogenetics and with karyotypes of neuroblastoma in patients without TS, in an attempt to localize the fragile site on the X chromosome. The ability to screen children at increased risk for neuroblastoma and an understanding of the molecular abnormalities which give rise to this disease may lead to improved outlook through early intervention and gene therapy.